EP0770639A2 - Use of polymers as auxiliary agents in drying aqueous polymer dispersions - Google Patents

Abstract

The process for drying aqueous dispersions of a polymer (B), in which the dispersion contains, as auxiliary drying agent, at least one polymer (A) containing (in polymerised form) 80-100 wt.% monomer(s) (a) of formula CH2CR1C(O)XCR2R3-R4-SOH (I) or salts thereof and 0-20 wt.% other radically polymerisable monomer(s) (b), in which R1-3 = H or 1-3 C alkyl; R4 = 1-5 C alkylene; and X = O or NH. Also claimed are: (i) the polymer powder containing (A) and (B); (ii) the mineral binder containing such polymer powder(s); (iii) the synthetic resin-plaster drying preparation containing such powder(s); (iv) the aqueous polymer dispersions of (B) with an emulsifier content of not more than 2 wt.%, containing (A) with a Mw of 5000-35,000 as added dispersant; (v) the process for the radical aqueous emulsion polymerisation of ethylenic monomers, in which (A) with a Mw of 5000-35000 is added before, during or after polymerisation; and (vi) the polymer powder obtained by drying as above.

Description

mit

R¹, R², R³:

unabhängig voneinander H oder C₁- bis C₃-Alkyl,

R⁴:

C₁- bis C₅-Alkylen und

X:

O oder NH,

und
zu 0 bis < 20 Gew.-% aus wenigstens einem radikalisch copolymerisierbaren Monomeren (Monomere b)
aufgebaut sind, als Hilfsmittel bei der Trocknung wäßriger Dispersionen von von den Polymerisaten I verschiedenen Polymerisaten II.The present invention relates to the use of polymers I in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With

R ¹ , R ² , R ³ :

independently of one another H or C ₁ to C ₃ alkyl,

R ⁴ :

C ₁ - to C ₅ alkylene and

X:

O or NH,

and
0 to <20% by weight of at least one radically copolymerizable monomer (monomers b)
are built up as aids in the drying of aqueous dispersions of polymers II other than polymers I.

In addition, the present invention relates to the polymer powders obtained in the course of drying, redispersible in water, and the use of these powders (for example as an additive in mineral binders or as binders in synthetic resin plasters) and dispersions of polymers II required for the preparation of the powders.

Aqueous polymer dispersions are generally known. These are systems which essentially contain spherical balls of intertwined polymer chains (so-called polymer particles) in disperse distribution. Just like polymer solutions when the solvent is evaporated, aqueous polymer dispersions have the potential to form polymer films when the aqueous dispersion medium is evaporated, which is why they are used in particular as binders, adhesives and coating agents. For the properties Aqueous polymer dispersions of central importance is the size of the polymer particles contained in them in disperse distribution. In particular properties such as the viscosity of the aqueous polymer dispersion or the gloss of its films are dependent on the diameter of the dispersed polymer particles or, more precisely, on the diameter distribution function of the dispersed polymer particles (films of small polymer particles generally have a higher gloss with identical polymer; a broad diameter distribution generally causes a lower viscosity of the aqueous polymer dispersion; dispersions of small polymer particles generally have a greater pigment binding capacity, etc.).

A disadvantage of the application form "aqueous polymer dispersion", however, is that its place of manufacture is generally different from the place of use. However, transporting them from the place of manufacture to the place of use always implies, in addition to the transport of the polymer which ultimately essentially constitutes the polymer film, the transport of the dispersing medium "water", which is readily available everywhere. Aqueous polymer dispersions can also be added to mineral binders for the purpose of modifying them only at the place of use, since these otherwise harden before use.

A desirable form of appearance of any aqueous polymer dispersion is therefore that of its polymer powder which is redispersed when water is added.

In principle, when water is added, redispersible polymer powders are accessible by drying their aqueous polymer dispersions. Examples of such drying processes are freeze drying and spray drying. The latter method, in which the polymer dispersion is sprayed and dewatered in a hot air stream, is particularly expedient for producing large amounts of powder. The dry air and the sprayed dispersion are preferably passed through the dryer in cocurrent (cf. e.g. EP-A 262326 or EP-A 407889).

A disadvantage of the polymer powders produced by drying aqueous polymer dispersions, however, is that their redispersibility when water is added is generally not fully satisfactory insofar as the polymer particle diameter distribution resulting from the redispersion is generally different from that in the aqueous starting dispersion (primary particle diameter distribution) .

This fact arises from the fact that aqueous polymer dispersions do not form thermodynamically stable systems. Rather, the system tries to reduce the polymer / dispersion medium interface by combining small primary particles into larger secondary particles (e.g. specks, coagulate), which can be prevented for a long time in the state of disperse distribution in the aqueous medium by adding dispersant. In the course of drying, however, the separating effect of the dispersing agents is often no longer sufficient and to a certain extent irreversible secondary particle formation occurs. This means that the secondary particles are retained as such during redispersion and reduce the performance properties of the aqueous polymer dispersion obtainable as part of the redispersion.

It has long been known that there are substances whose addition to aqueous polymer dispersions reduces the appearance of irreversible secondary particle formation when drying. These substances are summarized under the generic term drying aids. They are widely known in particular as spraying aids, since spray drying promotes the formation of irreversible secondary particles to a particular extent. At the same time, they generally reduce the formation of polymer coating adhering to the dryer wall during spray drying, thus increasing the powder yield.

From EP-A 629650 it is known that polymers (polymers III) obtained by radical polymerization of monomer mixtures of 15 to 80% by weight of at least one monomer of the general formula I and 20 to 85% by weight of radically copolymerizable monomers in aqueous Medium are available as spray aids in the spray drying of aqueous polymer dispersions are suitable. US-3965032 relates to the use of polymers III as dispersants in aqueous polymer dispersions. A disadvantage of the polymers III of EP-A 629650, however, is that they cannot fully satisfy their use as auxiliaries in the drying of aqueous polymer dispersions.

It was therefore an object of the present invention to provide the use of auxiliaries which are more suitable for drying aqueous polymer dispersions. Accordingly, the use of polymers I defined at the outset was found.

Polymers I and processes for their preparation in a wide variety of molecular weights are generally known.

JP-A 2/173108 describes e.g. the production of homopolymers and copolymers of 2-acrylamido-2-methylpropanesulfonic acid and its salts. JP-A 2/173108 sees solely the use as a dispersant for inorganic materials in an aqueous medium as a possible application for these polymers.

US Pat. No. 5,294,686 discloses a process for the preparation of low molecular weight 2-acrylamido-2-methylpropanesulfonic acid polymers and their use as dispersants and corrosion inhibitors.

JP-A 6/122842 relates to the production of polymers I and their use as an additive in underwater antifouling agents.

US Pat. No. 3,936,400 recommends low molecular weight 2-acrylamido-2-methylpropanesulfonic acid polymers as viscosity regulators in oil production.

AU-A 35611/84 relates to water-soluble polymers which contain carboxyl, sulfate or sulfonic acid groups and are terminated by -OH, -COOH or C _1-3 alkyl groups. These polymers are recommended as dispersants for particulate materials.

EP-A 123329 recommends inter alia Copolymers of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as dispersants in aqueous pigment dispersions.

US-469816 discloses the use of a mixture of two polymers for the dispersion of a material consisting of particles. One of the copolymers is polyacrylic acid, the other is poly-2-acrylamido-2-methylpropanesulfonic acid.

DE-A 3232811 relates to the production of microcapsules with polyurea capsule walls in the presence of special polymers containing sulfonic acid groups. As such, homopolymers of 2-acrylamido-2-methylpropanesulfonic acid with a relative molecular weight of 5000 to 10 ⁷ are used.

EP-A 511520 recommends inter alia the use of polymers I as dispersants for the preparation of emulsifier-free aqueous polymer dispersions.

Polymers I to be used according to the invention preferably contain copolymerized monomers a in which R ¹ , R ² , R ³ , independently of one another, is H or CH ₃ . Furthermore, monomers a of Advantage where X is NH. C ₁ -C ₃ -alkylene is advantageous as R ⁴ . A 2-acrylamido-2-methylpropanesulfonic acid (or its salts) is very particularly preferably used as the monomer, ie the monomer of the general formula I in which R ¹ = H, R ² and R ³ = CH ₃ , R ⁴ = -CH ₂ - and X = NH.

Suitable monomers a in salt form are in particular alkali metal (e.g. Li, Na, K) and alkaline earth metal (Ca, Mg) salts, but also salts which can be obtained by neutralizing the free acid by means of organic amines or ammonia. Polymers I suitable in the sense of the invention are e.g. those whose weight fraction of polymerized monomers a is at least 85, or at least 90, or at least 95 or 100% by weight.

Suitable monomers b are all radically polymerizable monomers different from monomers a. These are, for example, monoethylenically unsaturated monomers such as olefins, for example ethylene or propylene, vinylaromatic monomers such as styrene, α-methylstyrene, o-chlorostyrene or vinyltoluenes, esters of vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms such as vinyl acetate, vinyl propionate, vinyl-n- butyrate, vinyl laurate and vinyl stearate, esters of α, β-monoethylenically unsaturated mono- and dicarboxylic acids, preferably having 3 to 6 carbon atoms, such as acrylic acid, methacrylic acid, fumaric acid and itaconic acid, with generally 1 to 12, often 1 to 8 and mostly 1 alkanols containing up to 4 carbon atoms such as, in particular, methyl, ethyl, n-butyl, isobutyl, tert-butyl and 2-ethylhexyl acrylate, dimethyl maleate or n-butyl maleate , the nitriles of the aforementioned α, β-monoethylenically unsaturated carboxylic acids such as acrylonitrile and C _4-8 -conjugated dienes such as 1,3-butadiene and isoprene. Further suitable monomers b are α, β-monoethylenically unsaturated mono- and dicarboxylic acids and their amides such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, the monoesters of these carboxylic acids with polyhydric alcohols such as hydroxyethyl acrylate, having 3 to 6 carbon atoms , Hydroxypropyl acrylate, also vinyl sulfonic acid and N-vinyl pyrrolidone.

_w von erfindungsgemäß zu verwendenden Polymerisaten I (bezogen auf die vollneutraliesierte Na-Salz Form) kann z.B. 1000 bis 10⁶, aber auch 2000 bis 5·10⁵ oder 5000 bis 10⁵ oder 1000 bis 45000 oder 7500 bis 35000 oder 10 000 bis 25 000 betragen.If the polymer I to be used according to the invention contains no monomers b polymerized in, it will generally be a homopolymer of a monomer I, for example 2-acrylamido-2-methylpropanesulfonic acid or one of its salts. The weight average relative molecular weight $\overline{\text{M}}$

_w of polymers I to be used according to the invention (based on the fully neutralized Na salt form) can be, for example, 1000 to 10 ⁶ , but also 2000 to 5 · 10 ⁵ or 5000 to 10 ⁵ or 1000 to 45000 or 7500 to 35000 or 10,000 to 25,000.

• 1. Innendurchmesser : 7,8 mm, Länge : 30 cm, Trennmaterial : Toso Hass TSK PW-XL 5000,
• 2. Innendurchmesser : 7,8 mm, Länge : 30 cm, Trennmaterial : Waters Ultrahydrogel 1000,
• 3. Innendurchmesser : 7,8 mm, Länge : 30 cm, Trennmaterial : Waters Ultrahydrogel 500,
• 4. Innendurchmesser : 7,8 mm, Länge : 30 cm, Trennmaterial : Waters Ultrahydrogel 500.

In the case of the generally water-soluble Na salts of the polymers I, the reference basis for the above-mentioned information is a molecular weight determination according to the gel permeation chromatography method using four columns arranged in series

• 1.Inside diameter: 7.8 mm, length: 30 cm, separating material: Toso Hass TSK PW-XL 5000,
• 2.Inside diameter: 7.8 mm, length: 30 cm, separating material: Waters Ultrahydrogel 1000,
• 3. Inner diameter: 7.8 mm, length: 30 cm, separating material: Waters Ultrahydrogel 500,
• 4.Inside diameter: 7.8 mm, length: 30 cm, separating material: Waters Ultrahydrogel 500.

200 .mu.l of a 0.1% by weight aqueous solution of the polymer I neutralized with sodium hydroxide are added. The columns are heated to 35.degree. An aqueous 0.08 molar solution of a TRIS buffer (pH 7) is used as eluent, to which 0.15 mol / l NaCl or 0.01 mol / l NaN _{3 are} added. The flow rate of the eluent is chosen to be 0.5 ml / min. Before the sample is placed, the sample is filtered through a Sartorius Minisart RC 25 filter (pore size 0.20 µm). A ERC 7510 differential refractometer from ERMA is used as the detector. The calibration is carried out according to R. Brüssau and others in Tenside, Surf.Det. 28 : 396-406 (1991). Relative molecular weights <700 are not taken into account in the aforementioned determination method.

As already mentioned, the preparation of polymers to be used according to the invention is known per se. It is advantageously carried out by radical polymerization. This is preferably carried out in polar solvents, in particular in water. Both the free acids and their corresponding water-soluble salts can be used as monomers a. Of course, their mixtures can also be used. Substances which regulate the molecular weight can also be used to set the desired molecular weight. Suitable molecular weight regulators are compounds which have a thiol group (for example tert-dodecyl or n-dodecyl mercaptan).

_w zu zahlenmittlerem Molekulargewicht $\overline{\text{M}}$

_n der erfindungsgemäß zu verwendenden wäßrigen Polymerisate I kann 1 bis 30 bzw. 1 bis 20 oder 1 bis 8 betragen. D.h., das Molekulargewicht kann im wesentlichen einheitlich oder über eine gewisse Breite verteilt sein.Suitable starters are inorganic peroxides such as sodium peroxodisulfate. Depending on the monomer composition, the polymerization can be carried out as solution or emulsion polymerization. The ratio of weight average molecular weight $\overline{\text{M}}$

_w to number average molecular weight $\overline{\text{M}}$

_{n of} the aqueous polymers I to be used according to the invention can be 1 to 30 or 1 to 20 or 1 to 8. That is, the molecular weight can be essentially uniform or distributed over a certain width.

It is advantageous if the polymers I to be used according to the invention dissolve in 100 g of water at 25 ° C. and 1 bar to at least 1 g. As a rule, this will be the case. Frequently, the solubility of the polymers I to be used according to the invention in 100 g of water under the aforementioned conditions is at least 10 g.

If the redispersible polymer powder is prepared by the spray drying process, the polymer to be used according to the invention will generally be chosen so that its glass transition temperature (midpoint temperature, ASTM D 3418-82) is above the glass transition temperature of polymer II of the aqueous polymer dispersion to be spray-dried.

It is particularly expedient to spray-dry an aqueous polymer dispersion at an inlet temperature T _{E of} the hot air stream of 100 to 200 ° C, preferably 120 to 160 ° C, and an outlet temperature T _{A of} the warm air stream of 30 to 90 ° C, preferably 50 to 70 ° C to perform. The aqueous polymer dispersion can be sprayed in a hot air stream, for example by means of single or multi-component nozzles or via a rotating disk. The polymer powders are normally separated off using cyclones or filter separators. The sprayed aqueous polymer dispersion and the hot air stream are preferably conducted in parallel.

Against this background, preferred spray aids are those polymers I whose glass transition temperature meets the condition> T _A. According to our own investigations, the glass transition temperatures of homopolymers of the monomers a are above 100 ° C. for not too low molecular weights.

The polymer I to be used according to the invention can be added directly to the aqueous dispersion of the polymer II to be dried as an aqueous solution or as an aqueous dispersion. In the case of an aqueous solution of polymer I to be used the aqueous dispersion of polymer II is preferably stirred into the aqueous solution of polymer I.

It is surprising that addition of polymers I in amounts of 1 or 2 to 5% by weight, based on the amount of polymer II contained in the dispersion to be dried, already requires good redispersibility of the polymer powder resulting from drying.

Of course, in the same way, the polymers I to be used according to the invention can also be used in amounts of 1 to 10% by weight or 5 to 40% by weight or more, or in amounts of 10 to 20% by weight .

• A) 80 bis 100 Gew.-% wenigstens eines Monomeren aus der Gruppe umfassend Styrol, α-Methylstyrol, Vinyltoluole, Ester aus 3 bis 6 C-Atome aufweisenden α,β-monoethylenisch ungesättigten Carbonsäuren und 1 bis 12 C-Atome aufweisenden Alkanolen, Butadien sowie Vinyl- und Allylester von 1 bis 12 C-Atome aufweisenden Carbonsäuren und
• B) 0 bis 20 Gew.-% sonstigen, wenigstens eine ethylenisch ungesättigte Gruppe aufweisenden Monomeren

aufgebaut sind (solche Polymerisate II seien nachfolgend als Polymerisate II* bezeichnet). D.h., mögliche Monomere A sind n-Butylacrylat, 2-Ethylhexylacrylat, Methylmethacrylat und Styrol.The use of polymers I according to the invention has proven to be particularly favorable in the case of polymers II whose glass transition temperature is 25 50 ° C. or ° 25 ° C. or ° 0 ° C. As a rule, the glass transition temperature of polymer II will be ≥ - 60 ° C, or ≥ - 40 ° C or ≥ - 20 ° C. Furthermore, the use of polymers I according to the invention proves to be particularly advantageous in the case of those polymers II which are in polymerized form

• A) 80 to 100% by weight of at least one monomer from the group comprising styrene, α-methylstyrene, vinyltoluenes, esters of 3 to 6 C-atom-containing α, β-monoethylenically unsaturated carboxylic acids and 1 to 12 C-atom alkanols, Butadiene and vinyl and allyl esters of 1 to 12 carbon atoms and carboxylic acids
• B) 0 to 20% by weight of other monomers having at least one ethylenically unsaturated group

are built up (such polymers II are referred to below as polymers II *). Ie, possible monomers A are n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate and styrene.

Possible monomers B are acrylamide, methacrylamide, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, 2-acrylamido-2-methylpropanesulfonic acid, vinyl pyrrolidone, hydroxyethyl acrylate, hydroxymethylacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, quaternized vinylimidazole, N, N-meth (N) dialkyl, N, N (N) dialkyl Dialkylaminoalkyl (meth) acrylamides, Trialkylammoniumalkyl (meth) acrylates and Trialkylammoniumalkyl (meth) acrylamides.

Of course, the polymer dispersion to be dried can be a secondary dispersion of a polymer II. In this case the polymer II is e.g. prepared in a manner known per se by the method of free-radical solution polymerization and subsequently converted into an aqueous polymer dispersion. In this case, the polymer I is preferably added to the finished aqueous polymer dispersion which contains the polymer II in dispersed form.

If the aqueous polymer dispersion comprising polymer II is a primary dispersion, i.e. In order to add such a polymer dispersion, which is produced directly in disperse distribution by the free-radical aqueous emulsion polymerization method, the polymer I to be used according to the invention can be added as a drying aid both before, during and / or after the emulsion polymerization of the monomers constituting the polymer II.

In other words, polymer I will generally be added to an aqueous dispersion of polymer II which already contains dispersing agents (usually in amounts of up to 3% by weight, based on the amount of polymer II). Both the commonly used protective colloids and emulsifiers, such as those e.g. are named in DE-A 4 21 39 65. The stabilizing effect of protective colloids is primarily due to steric and / or electrostatic shielding of the dispersed polymer particles. As a rule, these are substances whose molecular weight is above 1500. They can be bound to the dispersed polymer particles both chemically and only physically. The stabilizing effect of emulsifiers, whose relative molecular weight is regularly <1000, is due to the fact that they are able to reduce the interfacial tension of the polymer / aqueous dispersion medium interface due to their amphiphilic structure (polar part and non-polar part). In contrast to protective colloids, emulsifiers can form micelles in water. They are also designed so that when added to water at 25 ° C and 1 atm, when the critical micelle concentration is reached, they reduce its surface tension by at least 25%.

It is very important according to the invention that in particular polymers I to be used according to the invention (in particular if they contain no monomers b polymerized in), whose weight average relative molecular weight is 5,000 to 35,000, preferably 7,500 to 20,000 or 15,000, not only form drying aids which can be used according to the invention, but at the same time are able to stabilize the disperse distribution of aqueous polymer dispersions in an outstanding manner. That is, if such polymers I to be used according to the invention are added during the course of the free radical aqueous emulsion polymerization, on the one hand there is the possibility of producing aqueous polymer dispersions of polymers II whose emulsifier content, based on the amount of dispersed polymer II, is ≤ 2 or ≤ 1 or ≤ 0.5 or ≤ 0.1 or 0 wt .-% (the use of emulsifiers is often undesirable, since they usually make the films of the aqueous polymer dispersion sensitive to the action of water or, due to their low molecular weight, usually from the Sweat out filming), and which, on the other hand, can be dried in an excellent way to redispersible polymer powders. It is not necessary for the aqueous dispersion of polymer II to contain, in addition to polymers I, other types of protective colloids added in the course of their preparation. Rather, the content of protective colloids other than polymer I, based on the amount of polymer II contained, can be 5 5% by weight or 3 3% by weight or 0% by weight.

It is particularly noteworthy that the use of such low molecular weight polymers I as described above also enables the production of stable, finely divided (weight-average polymer particle diameters 500 500 nm, frequently ≤ 200 nm and 50 50 nm) aqueous polymer dispersions of polymers II. It is noteworthy that in this regard the use of ≥ 1% by weight to ≤ 10% by weight of low molecular weight polymer I, based on polymer II to be dispersed, is sufficient, particularly when it is a matter of low molecular weight poly-2-acrylamido-2 -methylpropanesulfonic acid acts as polymer I (of course, however, use amounts of up to 25 or up to 50% by weight can also be used in a corresponding manner). This fact is surprising even in view of the recommendation in the prior art to use low molecular weight polymers I as dispersants for finely divided inorganic materials. As is shown in the exemplary embodiments, it cannot normally be concluded from a dispersing action in the case of finely divided inorganic materials that such an action is involved in the preparation of aqueous polymer dispersions by the free-radical aqueous emulsion polymerization method.

The monomer composition of polymer II is essentially irrelevant with regard to the aforementioned relationships. The same applies to the type of emulsifiers and protective colloids used, as well as to the type of polymerization initiator used. That is, the above-mentioned relationships meet e.g. also in the case of those polymers II which contain less than 70% by weight of styrene copolymerized.

MaW come as monomers having at least one ethylenically unsaturated group to build up the polymer II in the aforementioned context, including other monoethylenically unsaturated monomers such as olefins, for example ethylene, vinylaromatic monomers such as styrene, α-methylstyrene, o-chlorostyrene or vinyltoluenes, vinyl and vinylidene halides such as vinyl and vinylidene chloride, esters of vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate, esters of α, β-monoethylenically unsaturated mono preferably having 3 to 6 carbon atoms and dicarboxylic acids, such as, in particular, acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, with alkanols which generally have 1 to 12, preferably 1 to 8 and in particular 1 to 4, carbon atoms, such as, in particular, methyl, ethyl, acrylic acid and methacrylic acid, n-butyl, isobutyl and -2-ethylhexyl ester, dimethyl maleate or Ma n-butyl linseate, nitriles α, β-monoethylenically unsaturated carboxylic acids such as acrylonitrile and C _4-8 -conjugated dienes such as 1,3-butadiene and isoprene. The monomers mentioned generally form the main monomers which, based on the total amount of the monomers to be polymerized by the process of free-radical aqueous emulsion polymerization, normally comprise a proportion of more than 50% by weight. Monomers which, when polymerized on their own, usually give homopolymers which have an increased solubility in water, are normally only used as modifying monomers in amounts, based on the total amount of the monomers to be polymerized, of less than 50% by weight, generally 0.5 up to 20, preferably 1 to 10 wt .-%, co-polymerized.

Examples of such monomers are α, β-monoethylenically unsaturated mono- and dicarboxylic acids and their amides such as, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, also vinyl sulfonic acid and its water-soluble salts and N- Vinyl pyrrolidone. Monomers, which usually increase the internal strength of the films in the aqueous polymer dispersion, are also generally only used in minor amounts, usually 0.5 to 10% by weight, based on the total amount of those to be polymerized Monomers, co-polymerized. Such monomers normally have an epoxy, hydroxyl, N-methylol, carbonyl group or at least two non-conjugated ethylenically unsaturated double bonds. Examples of these are N-alkylolamides of α, β-monoethylenically unsaturated carboxylic acids having 3 to 10 C atoms and their esters with alcohols having 1 to 4 C atoms, among which the N-methylolacrylamide and the N-methylolmethacrylamide are very particularly preferred, two monomers having vinyl radicals, two monomers having vinylidene radicals and two monomers having alkenyl radicals. The di-esters of dihydric alcohols with α, β-monoethylenically unsaturated monocarboxylic acids are particularly suitable, among which in turn acrylic and methacrylic acid are preferably used. Examples of such two nonconjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates monomers such as ethylene glycol, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate and propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, Cyclopentadienylacrylat or triallyl cyanurate. In this context, the methacrylic acid and acrylic acid C ₁ -C ₈ hydroxyalkyl esters such as n-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl acrylate and methacrylate as well as compounds such as diacetone acrylamide and acetylacetoxyethyl acrylate or methacrylate are also of particular importance. In addition to monomers having unsaturated double bonds, minor amounts, usually 0.01 to 2% by weight, based on the monomers to be polymerized, of copolymerizing substances such as tert-dodecyl mercaptan and 3-mercaptopropyltrimethoxysilane can also be copolymerized. Such substances are preferably added to the polymerization zone in a mixture with the monomers to be polymerized.

Above all, the particular suitability of the low molecular weight polymers I as essentially the sole dispersant in the context of the radical aqueous emulsion polymerization preparation of polymers II applies in the case of the polymers II *.

This means that the use of polymers I according to the invention in particular enables both the preparation of emulsifier-free aqueous polymer dispersions and the preparation of emulsifier-free polymer powders redispersible in water. It is noteworthy that such essentially emulsifier-free aqueous polymer dispersions are characterized by a reduced viscosity.

When carrying out the free radical aqueous emulsion polymerization for the preparation of aqueous dispersions of polymers II, the disperse distribution of which is essentially stabilized by means of polymers I, the method of the monomer feed is preferably used. The total amount of polymer I to be used as a protective colloid can either be placed in the polymerization vessel or continuously fed to the polymerization vessel together with the monomers to be polymerized.

It should be noted that in the context of the use according to the invention, in addition to the polymers I to be used according to the invention, drying aids known per se (e.g. polyvinyl alcohol, polyvinyl pyrrolidone, naphthalenesulfonic acid (or phenolsulfonic acid) -formaldehyde condensates etc.) can also be used. The same applies to anti-caking agents such as highly disperse silicic acid, which are often used in the context of spray drying to prevent the polymer powder from caking during storage.

The polymer powders resulting from use according to the invention are suitable as binders in hydraulically setting compositions, paints, varnishes, adhesives, coating compositions (in particular for paper) and synthetic resin plasters, as are described in EP-A 629650. The same applies to the initial dispersions used for powder production. Their solids volume content can be 10 to 75, often 20 to 65, mostly 30 to 50 vol .-%, based on the volume of the polymer dispersion.

In conclusion, it should be noted that when an aqueous solution or dispersion of a polymer I and an aqueous dispersion of a polymer II are combined, compatibility must be ensured. In other words, in the case of a cationically stabilized aqueous dispersion of a polymer II, no anionic polymer I system should be added.

Examples

Zulauf I:

280 g Methylmethacrylat und
1 g Ester aus Thioglykolsäure und 2-Ethylhexanol;

Zulauf II:

120 g 2-Acrylamido-2-methylpropansulfonsäure
400 g Wasser und
150 g 20 gew.-%ige wäßrige Natriumhydroxidlösung;

Zulauf III:

15,84 g Natriumperoxodisulfat und
150 g Wasser.

Der Feststoffgehalt der resultierenden wäßrigen Polymerisatdispersion betrug 20 Gew.-%.
c) Herstellung von sprühzutrocknenden wäßrigen Standarddispersionen von Polymerisaten II (SDII1 bis SDII4)

SDII1:

Entspricht Beispiel 2, DPIIa der EP-A 629650

In einem Polymerisationsgefäß wurde eine Lösung aus

294 g

Wasser

7,7 g

einer 10 gew.-%igen wäßrigen Ameisensäurelösung

6,6 g

einer 20 gew.-%igen wäßrigen Lösung von Polyacrylamid

3,3 g

Natriumhydrogencarbonat

11 g

einer 20 gew.-%igen wäßrigen Lösung von ethoxyliertem p-Isooctylphenol (EO-Grad: 25) = Emulgatorlösung 1 und

0,9 g

einer 35 gew.-%igen wäßrigen Lösung des Na-Salzes des Schwefelsäurehalbesters von ethoxyliertem p-Isooctylphenol (EO-Grad: 25) = Emulgatorlösung 2

vorgelegt und auf die Polymerisationstemperatur von 90°C erwärmt. Anschließend wurden zeitgleich beginnend die Zuläufe I (innerhalb von 2 h) und II (innerhalb von 2,5 h) unter Aufrechterhaltung der Polymerisationstemperatur dem Polymerisationsgefäß kontinuierlich zugeführt. Danach wurde das Polymerisationsgefäß weitere 2 h bei 90°C sich selbst überlassen. Anschließend wurde auf Raumtemperatur abgekühlt und mit 5,5 g einer 20 gew.-%igen wäßrigen Calciumhydroxid-Aufschlämmung neutralisiert. Der Feststoffgehalt der resultierenden wäßrigen Polymerisatdispersion SDII1 betrug 54,7 Gew.-%. Das dispergierte Polymerisat wies eine Glasübergangstemperatur von -1°C auf.

• Zulauf I:

  682 g

  n-Butylacrylat

  385 g

  Styrol

  44 g

  einer 50 gew.-%igen wäßrigen Lösung von Acrylamid

  73,3 g

  einer 15 gew.-%igen wäßrigen Lösung von Methacrylamid

  16,5 g

  Emulgatorlösung 1

  22,6 g

  Emulgatorlösung 2 und

  235 g

  Wasser.

• Zulauf II:

  6,4 g

  Natriumperoxidisulfat in

  180 g

  Wasser.

  SDII2:

  Entspricht Beispiel 2, DPIIb der EP-A 629650

In einem Polymerisationsgefäß wurde eine Mischung aus

500 g

Wasser

2,5 g

Natriumacetat

2,5 g

Butenol und

10 g

einer ethoxylierten Cellulose (Natrosol® 250 GR)

auf die Polymerisationstemperatur von 80°C erwärmt. Dann wurden auf einmal zunächst 150 g Zulauf I und danach 10 g Zulauf II in das Polymerisationsgefäß eingetragen und 20 min. bei 80°C polymerisiert. Anschließend wurde zeitgleich beginnend die Restmenge von Zulauf I (innerhalb von 3 h) und die Restmenge von Zulauf II (innerhalb von 3,5 h) unter Aufrechterhaltung der 80°C kontinuierlich zudosiert. Danach wurde noch 1 h bei 80°C gerührt und schließlich auf Raumtemperatur abgekühlt.
Der Feststoffgehalt der resultierenden wäßrigen Polymerisatdispersion SDII2 betrug 50,2 Gew.-%. Das dispergierte Polymerisat wies eine Glasübergangstemperatur von -2°C auf.

• Zulauf I:

  600 g

  Vinylpropionat

  200 g

  tert.-Butylacrylat

  200 g

  n-Butylacrylat

  160 g

  eines Gemisches aus 150 g Emulgatorlösung 1 und 10 g eines Blockcopolymeren aus Ethylenoxid und Propylenoxid (molares Verhältnis EO:PO = 0,7 und das relative zahlenmittlere Molekulargewicht = 3200) und

  343 g

  Wasser;

• Zulauf II:

  5 g

  Natriumperoxidisulfat in

  100 g

  Wasser.

  SDII3:

  Entspricht Beispiel 3, DPIIc der EP-A 629650

In einem Polymerisationsgefäß wurde eine Lösung aus

6000 g

Wasser und

17 g

einer 45 gew.-%igen wäßrigen Lösung der Dowfax® 2A1 entsprechenden grenzflächenaktiven Substanz

auf die Polymerisationstemperatur von 80⁰C erwärmt. Anschließend wurden nacheinander auf einmal 1087 g Zulauf I und 108 g Zulauf II ins Polymerisationsgefäß gegeben und 30 min. bei 80°C polymerisiert. Anschließend wurden unter Aufrechterhaltung der Polymerisationstemperatur die Restmengen der Zuläufe I und II zeitgleich beginnend während 3,5 h kontinuierlich zugeführt. Anschließend wurde das Reaktionsgemisch 4 h bei 80°C sich selbst überlassen. Abschließend wurde auf Raumtemperatur abgekühlt und mit 420 g einer 25 gew.-%igen wäßrigen Natriumhydroxidlösung neutralisiert. Der Festgehalt der resultierenden wäßrigen Polymerisatdispersion SDII3 betrug 50,9 Gew.-%. Das dispergierte Polymerisat wies eine Glasübergangstemperatur von 60°C auf.

• Zulauf I:

  12150 g

  Styrol

  2250 g

  Butadien

  450 g

  einer 50 %igen wäßrigen Lösung von Acrylamid

  375 g

  Acrylsäure

  120 g

  ter.-Dodecylmercaptan

  117 g

  einer 45 gew.-%igen wäßrigen Lösung der Dowfax 2A1 entsprechenden grenzflächenaktiven Substanz

  250 g

  einer 15 gew.-%igen wäßrigen Lösung des Natriumsalzes des Schwefelsäurehalbesters von Laurylalkohol und

  6033 g

  Wasser.

• Zulauf II:

  150 g

  Natriumperoxidisulfat und

  200 g

  Wasser.

  SDII4:

Wie SDII1, jedoch wurden die 385 g Styrol durch 385 g Methylmethacrylat ersetzt. Nach Filtration wurde eine Dispersion SDII4 mit einem Feststoffgehalt von 55,6 Gew.-% erhalten. Das dispergierte Polymerisat wies eine Glasübergangstemperatur von 0°C auf.
d) Sprühtrocknung der wäßrigen Polymerisatdispersionen aus c) und Beurteilung der Redispergierbarkeit der resultierenden Pulver
Zunächst wurde die jeweilige wäßrige Polymerisatdispersion SDII1 bis SDII4 auf einen Feststoffgehalt von 36,2 Gew.-% verdünnt. Dann wurde in die wäßrige Lösung des EPI1 aus a) bzw. in die wäßrige Dispersion des VPI aus a) unter kräftigem Rühren soviel der jeweiligen auf 36,2 Gew.-% verdünnten Polymerisatdispersion SDII1 bis SDII4 rasch eingerührt, daß ein wäßriges Gemisch resultierte, das einen Feststoffgehalt von 35 Gew.-% (bezogen auf das jeweilige dispergierte Polymerisat II waren somit stets 4,5 Gew.-% an EPI1 bzw. VPI enthalten) aufwies.
Die Sprühtrocknung der wäßrigen Gemische erfolgte in einem Minor-Labortrockner der Fa. GEA Wiegand GmbH (Geschäftsbereich Niro), DE, mit Zweistoffdüsenzerstäubung bei einer Turm-Eingangstemperatur von 130°C und einer -Ausgangstemperatur von 60°C (Leistung: ca. 2 kg Sprühspeise/h). Als Anti-Blockmittel wurden gleichzeitig mit der Sprühspeise ca. 2,5 Gew.-% (bezogen auf feste Polymerisat-Mischung) einer feinteiligen Kieselsäure (mittlerer Korngrößtdurchmesser: 10 µm) in die Trocknungskammer zudosiert. Die Beurteilung der jeweiligen Sprühtrocknung weist die Tabelle 1 aus.
Zur Überprüfung der Redispergierbarkeit der erhaltenen Polymerisatpulver wurde wie folgt vorgegangen:
In eine Glasflasche wurden 90 g Wasser eingewogen und bei 25°C mit 10 g Polymerisatpulver versetzt. Das Gemisch wurde mit einem Ultra-Turrax 1 der Fa. Janke & Kunkel, IKA-Labortechnik, Staufen DE, 1 min. bei 9500 U/min. gerührt und in einen Meßzylinder gefüllt. Anschließend wurde der mit einem Kunststoffstropfen verschlossene Meßzylinder bei 25°C 72 h unbewegt gelagert. Danach wurde die Redispersion gut geschüttelt und über ein 72-µm-Sieb filtriert. Das den Filterkuchen enthaltende Sieb wurde bei 80°C 12 h im Trockenschrank gelagert und anschließend durch Wägung der prozentuale Gewichtsanteil des getrockneten Koagulats, bezogen auf eingesetzte Pulvermenge (10 g), bestimmt. Die Ergebnisse zeigt ebenfalls die Tabelle 1. Tabelle 1 Sprühgetrocknetes Gemisch Wandbelag Pulverausbeute Koagulat Dispersion Sprühhilfsmittel SDII1 EPI1 wenig 86 % 0,5 Gew.-% SDII2 EPI1 wenig 74 % 1,4 Gew.-% SDII3 EPI1 wenig 63 % 2,2 Gew.-% SDII4 EPI1 wenig 89 % 0,7 Gew.-% SDII1 VPI1 stark 30 % 7,1 Gew.-%
e) Herstellung wäßriger Dispersionen von Polymerisaten II, die als im wesentlichen alleiniges Dispergiermittel ein niedermolekulares erfindungsgemäßes Polymerisat I enthalten, die Sprühtrocknung solcher wäßriger Polymerisatdispersionen und Vergleichsversuche

• D1:
  200 g n-Butylacrylat, 200 g Methylmethacrylat und 91,4 g der 19,7 gew.-%igen wäßrigen Lösung des Polymerisats EPI1 aus a) wurden in 114 g Wasser zu einem Zulauf 1 emulgiert. 12 g Natriumperoxodisulfat und 159 g Wasser bildeten den Zulauf 2.
  Unter Inertgasatmosphäre wurden in einem Polymerisationsgefäß 200 g Wasser sowie 5 Gew.-% des Zulaufs 1 vorgelegt. Die Vorlage wurde unter Rühren auf 90°C erhitzt und mit 10 Gew.-% des Zulaufs 2 versetzt. Anschließend wurde das Reaktionsgemisch 15 min. bei 90°C gehalten. Danach wurden dem Polymerisationsgefäß unter Aufrechterhaltung der 90°C die Restmenge an Zulauf 1 (innerhalb von 2 h) sowie die Restmenge an Zulauf 2 (innerhalb von 2,5 h) kontinuierlich zugeführt. Nach Beendigung der Zuläufe wurde das Reaktiongsgemisch noch 2 h bei 90°C gerührt und danach auf Raumtemperatur abgekühlt. Die nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltene wäßrige Polymerisatdispersion wies einen Feststoffgehalt von 43,6 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 1,9 sowie einen LD-Wert von 6 % auf (der LD-Wert ist ein Maß für die Polymerisatteilchengröße einer wäßrigen Polymerisatdispersion; er gibt die Lichtdurchlässigkeit bei 25°C im auf einen Feststoffgehalt von 0,01 Gew.-% verdünnten Zustand, relativ zu reinem Wasser und bei einer Schichtdicke von 2,5 cm an, unter Einstrahlung von weißem Licht). Im Filter blieben 0,2 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film zeigte im wesentlichen keine Stippen (Mikrokoagulat) auf.
• D2:
  Wie D1, mit dem Unterschied, daß der Zulauf 1 aus einer Emulsion von 208 g n-Butylacrylat, 180 g Methylmethacrylat, 8 g Acrylamid, 4 g Acrylsäure und 91,4 g der 19,7 gew.-%igen wäßrigen Lösung des Polymerisats EPI1 aus a) in 114 g Wasser bestand. Die nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 43,9 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 4,3 sowie einen LD-Wert von 52 % auf. Im Filter bleiben 0,2 g Koagulat zurück. Ein nasser, bei einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film zeigte im wesentlichen keine Stippen.
• D3:
  Wie D1, mit dem Unterschied, daß der Zulauf 1 aus einer Emulsion von 248 g n-Butylacrylat, 140 g Styrol, 8 g Acrylamid, 4 g Methacrylamid und 91,4 g der 19,7 gew.-%igen wäßrigen Lösung des Polymerisats EPI1 aus a) in 114 g Wasser bestand. Die nach Filtraten über ein Sieb mit einer Maschenweite von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 43,3 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 2,1 sowie einen LD-Wert von 49 % auf. Im Filter bleiben 0,3 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film zeigte im wesentlichen keine Stippen.
• D4:
  Aus einem Gemisch aus 100 g n-Butylacrylat und 100 g Methylmethacrylat wurde ein Zulauf 1 gebildet. Eine Lösung von 1,0 g Wasserstoffperoxid und 100 g Wasser bildete einen Zulauf 2. Unter Inertgasatmosphäre wurden in ein Polymerisationsgefäß 247 g Wasser, 1,3 g einer 15 gew.-%igen wäßrigen Natriumlaurylsulfat-Lösung, 50,8 g einer 19,7 gew.-%igen wäßrigen Lösung des Polymerisats EPI1 aus a), 0,04 g CuSO₄ · 5H₂O sowie 5 Gew.-% des Zulaufs 1 vorgelegt. Unter Rühren wurde die Vorlage auf 85°C erhitzt und mit 10 Gew.-% des Zulauf 2 versetzt. Danach wurde das Gemisch 15 min bei 85°C unter Rühren gehalten und anschließend unter Aufrechterhaltung der 85°C die Restmengen von Zulauf 1 (innerhalb von 2h) und Zulauf 2 (innerhalb von 2,5 h) zeitgleich beginnend kontinuierlich ins Polymerisationsgefäß zugeführt. Nach beendeter Zufuhr wurde das Polymerisationsgemisch noch 2 h bei 85°C nachgerührt und anschließend auf Raumtemperatur abgekühlt. Die nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 34,2 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 6,8 sowie einen LD-Wert von 88 % auf. Im Filter blieben 0,69 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film zeigte im wesentlichen keine Stippen.
• D5:
  Aus 155 g n-Butylacrylat, 87,5 g Styrol, 5 g Acrylamid, 2,5 g Methacrylamid, 190,4 g der 19,7 gew.-%igen Lösung des Polymerisats EPI1 aus a) und 20 g Wasser wurde eine Emulsion als Zulauf 1 gebildet. Eine Lösung von 7,5 g Natriumperoxodisulfat in 100 g Wasser bildete einen Zulauf 2. Unter Inertgasatmosphäre wurden in einem Polymerisationsgefäß 104 g Wasser, sowie 5 Gew.-% des Zulauf 1 vorgelegt. Die Vorlage wurde unter Rühren auf 90°C erhitzt und mit 10 Gew.-% des Zulaufs 2 versetzt. Anschließend wurde das Gemisch 15 min. unter Rühren bei 90°C gehalten. Anschließend wurden unter Aufrechterhaltung der 90°C, zeitgleich beginnend, die Restmengen von Zulauf 1 (innerhalb von 2,0 h) sowie von Zulauf 2 (innerhalb von 2,5 h) dem Polymerisationsgefäß kontinuierlich zugeführt. Danach wurde das Reaktionsgemisch noch 2 h bei 90°C gerührt und schließlich auf Raumtemperatur abgekühlt.
  Die nach Filtration über ein Sieb mit einer Maschenweit von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 43,2 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 2,7 sowie einen LD-Wert von 68 % auf. Im Filter blieben 0,3 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgrakelter Film zeigte im wesentlichen keine Stippen.
• VD1:
  Wie D1, Zulauf 1 bestand jedoch aus einer Emulsion von 200 g n-Butylacrylat, 200 g Methylmethacrylat und 90 g der 20 gew.-%igen wäßrigen Dispersion des Polymerisats VPI aus b) in 114 g Wasser. Die nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 43,4 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 1,7 sowie einen LD-Wert von 30 % auf. Im Filter blieben 5,8 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film wies zahlreiche Stippen auf.
• VD2:
  Wie D5, anstelle der 190,4 g der 19,7 gew.-%igen wäßrigen Lösung des Polymerisats EPI1 aus a) wurden jedoch 187,5 g der 20 gew.-%igen wäßrigen Dispersion des Polymerisats VPI aus b) eingesetzt. Die nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltene Dispersion wies einen Feststoffgehalt von 42,7 Gew.-%, einen pH-Wert ihres wäßrigen Dispergiermediums von 2,1 sowie einen LD-Wert von 43 % auf. Im Filter blieben 14 g Koagulat zurück. Ein nasser, in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelter Film wies zahlreiche Stippen auf.
• VD3:
  Wie D4, die Vorlage enthielt jedoch ein Gemisch aus 247 g Wasser, 1,3 g einer 15 gew.-%igen wäßrigen Natriumlaurylsulfatlösung, 50 g einer in Analogie zu a) hergestellten 20 gew.-%igen wäßrigen Lösung einer Poly-2-Acrylamido-2-methylpropansulfonsäure, deren gewichtsmittleres relatives Molekulargewicht jedoch 38 000 betrug, 0,04 g CuSO₄·5H₂O und 5 Gew.-% des Zulauf 1. Das Reaktionsgemisch verdickte bereits während des Monomerenzulaufs, so daß der Reaktionsansatz abgebrochen werden mußte.
• VD4:
  Wie D1, Zulauf 1 bestand jedoch aus 200 g n-Butylacrylat, 200 g Methylmethacrylat, 90 g der 20 gew.-%igen wäßrigen Poly-2-Acrylamido-2-methyl-propansulfonsäurelösung aus VD3 und 116 g Wasser. Der Ansatz koagulierte nach dem Auspolymerisieren.
• VD5:
  Wie D1, Zulauf 1 bestand jedoch aus 200 g n-Butylacrylat, 200 g Methylmethacrylat, 71,2 g einer 25,3 gew.-%igen wäßrigen Lösung von Sokalan® CP9 (Maleinsäure-Copolymer), das als Dispergiermittel für feinteilige organische und anorganische Feststoffe im Handel erhältlich ist und 135 g Wasser. Der Ansatz koagulierte nach dem Auspolymerisieren. Dies weist aus, daß Dispergiermittel für feinteilige organische und anorganische Feststoffe nicht notwendigerweise als Schutzkolloid zur Durchführung radikalischer wäßriger Emulsionspolymerisationen geeignet sind.
  Die wäßrigen Polymerisatdispersionen D1 bis D5 waren in befriedigender Weise nach dem unter d) beschriebenen Sprühtrocknungsverfahren zu redispergierbaren Polymerisatpulvern trockenbar.

f) Herstellung weiterer erfindungsgemäß zu verwendender Polymerisate I (EPI2 bis EPI6) sowie wäßriger Dispersionen D6 bis D10 von Polymerisaten II, die als im wesentlichen alleiniges Dispergiermittel ein niedermolekulares erfindungsgemäßes Polymerisat I enthalten und die Sprühtrocknung solcher wäßriger Polymerisatdispersionen.
1. Herstellung von EPI2 bis EPI6
Die Polymerisationen wurden unter Inertgas durchgeführt. In einem Polymerisationsgefäß wurden zunächst 810 g Wasser vorgelegt und auf 85°C erwärmt. Unter Aufrechterhaltung dieser Temperatur wurden 10 Gew.-% einer Lösung von Xg Natriumperoxodisulfat in Yg Wasser zugegeben und 5 min gerührt. Danach wurden unter Aufrechterhaltung der 85°C die Restmenge der Natriumperoxodisulfatlösung sowie, davon räumlich getrennt, eine Mischung aus 800 g Wasser, 400 g 2-Acrylamido-2-methylpropansulfonsäure, 400 g einer 25 gew.-%igen wäßrigen Natriumhydroxidlösung und 0,04 g 4-Methoxyphenol unter Rühren (beide Zuläufe zeitgleich beginnend) innerhalb von zwei Stunden dem Polymerisationsgefäß kontinuierlich zugeführt. Danach wurde das Reaktionsgemisch noch eine Stunde bei 85°C gerührt und anschließend abgekühlt. Die angewandten Werte für X und Y, die Feststoffgehalte der resultierenden wäßrigen Lösungen, die pH-Werte der zugehörigen wäßrigen Dispergiermedien und das gewichtsmittlere relative Molekulargewicht M_w der in Lösung befindlichen Polymerisate EPI2 bis EPI6 zeigt die nachfolgende Tabelle 1. Tabelle 1 X Y Feststoffgehalt (Gew.-%) pH-Wert M_w EPI2 2,4 100 19,3 13,5 12300 EPI3 5 110 19,2 13,4 11400 EPI4 10 130 19,4 13,4 10000 EPI5 20 170 19,5 13,2 9600 EPI6 40 250 19,3 12,9 8500
2. Herstellung wäßriger Dispersionen D6 bis D10 von Polymerisaten II und deren Sprühtrocknung
208 g n-Butylacrylat, 180 g Methylmethacrylat, 8 g Acrylamid, 4 g Acrylamid und 18,0 g eines der Polymerisate EPI2 bis EPI6 wurden in 187 g Wasser zu einem Zulauf 1 emulgiert und die resultierende Emulsion mittels 2N wäßriger NH₃-Lösung auf einen pH-Wert von 8,0 eingestellt. Die Lösung von 12,0 g Natriumperoxodisulfat in 159 g Wasser bildete den Zulauf 2.
Unter Intertgasatmosphäre wurden in einem Polymerisationsgefäß 200 g Wasser sowie 5 Gew.-% des Zulaufs 1 vorgelegt. Die Vorlage wurde unter Rühren auf 90°C erhitzt und mit 10 Gew.-% des Zulaufs 2 versetzt. Anschließend wurde das Reaktionsgemisch 15 min bei 90°C gehalten. Danach wurden dem Polymerisationsgefäß unter Aufrechterhaltung der 90°C die Restmenge an Zulauf 1 (innerhalb von 2 h) sowie die Restmenge an Zulauf 2 (innerhalb von 2,5 h) kontinuierlich zugeführt. Nach Beendigung der Zuläufe wurde das Reaktionsgemisch noch 2 h bei 90°C gerührt und danach auf Raumtemperatur abgekühlt. Von den nach Filtration über ein Sieb mit einer Maschenweite von 250 µm erhaltenen wäßrigen Polymerisatdispersionen wurden der Feststoffgehalt, der pH-Wert des wäßrigen Dispergiermediums sowie ihr LD-Wert und der Koagulatgehalt im Filter bestimmt. Zusätzlich wurde von den filtrierten wäßrigen Polymerisatdispersionen ein nasser Film in einer Schichtdicke von 60 µm auf eine Glasplatte aufgerakelt und an selbigem der Anteil an Stippen qualitativ (i.w. = im wesentlichen) beurteilt. Die erhaltenen Ergebnisse weist Tabelle II aus. Tabelle II Polymerisat I Feststoffgehalt [Gew.-%] LD [%] Koagulat [g] Steppen pH D6 EPI2 43,6 52 0,2 i.w. keine 4,7 D7 EPI3 43,1 53 0,5 i.w. keine 4,6 D8 EPI4 43,2 42 0,7 i.w. keine 4,5 D9 EPI5 43,8 34 0,6 i.w. keine 4,4 D10 EPI6 43,6 45 0,5 i.w. keine 4,4
a) Preparation of a Polymer I (EPI1) to be Used According to the Invention
The polymerization was carried out under an inert gas atmosphere. 820 g of water were initially placed in a polymerization vessel and heated to 85.degree. While maintaining this temperature, 10% by weight of a solution of 17.6 g of sodium peroxodisulfate in 150 g of water were added and 5 minutes. touched. The remaining amount of the sodium peroxodisulfate solution and, spatially separated therefrom, a mixture of 800 g of water, 400 g of 2-acrylamido-2-methylpropanesulfonic acid, 400 g of a 25% by weight aqueous sodium hydroxide solution and 0.04 g of 4 were then spatially separated -Methoxyphenol (polymerization retarder) with stirring (both feeds starting at the same time) continuously fed to the polymerization vessel within one hour. The reaction mixture was then stirred at 85 ° C. for one hour. The mixture was then cooled to 60 ° C. and a solution of 7.5 g of sodium hydroxymethyl sulfinate and 30 g of water was added with stirring in the course of one hour (in order to remove remaining peroxide).
The resulting clear solution had a solids content of 19.7% by weight and a pH of 12.8. The weight average relative molecular weight of the dissolved polymer EPI1 was determined to be 10,000.
b) Preparation of a Comparative Polymer I (VPI) recommended as a spraying aid in EP-A 629650 (Example 1, DPIa)
The polymerization was carried out under an inert gas atmosphere. A solution of 1.76 g of sodium peroxodisulfate in 1050 g of water was placed in a polymerization vessel and heated to the polymerization temperature of 85.degree. Subsequently, while maintaining the polymerization temperature, feeds I to III were fed synchronously to the polymerization vessel, starting simultaneously, within 2 h. The reaction mixture was then left to stand at 85 ° C. for 1 h. 3 g of a 20% strength by weight aqueous solution of the sodium metal salt of hydroxymethanesulfinic acid were then added and the mixture was cooled to room temperature.

Inlet I:

280 g of methyl methacrylate and
1 g ester of thioglycolic acid and 2-ethylhexanol;

Inlet II:

120 g of 2-acrylamido-2-methylpropanesulfonic acid
400 g water and
150 g of 20% by weight aqueous sodium hydroxide solution;

Inlet III:

15.84 g sodium peroxodisulfate and
150 g water.

The solids content of the resulting aqueous polymer dispersion was 20% by weight.
c) Preparation of spray-dried aqueous standard dispersions of polymers II (SDII1 to SDII4)

SDII1:

Corresponds to Example 2, DPIIa of EP-A 629650

A solution was made in a polymerization vessel

294 g

water

7.7 g

a 10 wt .-% aqueous formic acid solution

6.6 g

a 20 wt .-% aqueous solution of polyacrylamide

3.3 g

Sodium bicarbonate

11 g

a 20% by weight aqueous solution of ethoxylated p-isooctylphenol (EO grade: 25) = emulsifier solution 1 and

0.9 g

a 35% by weight aqueous solution of the sodium salt of the sulfuric acid half-ester of ethoxylated p-isooctylphenol (EO grade: 25) = emulsifier solution 2

submitted and heated to the polymerization temperature of 90 ° C. Subsequently, feeds I (within 2 hours) and II (within 2.5 hours) were continuously fed into the polymerization vessel while maintaining the polymerization temperature. The polymerization vessel was then left to stand at 90 ° C. for a further 2 h. It was then cooled to room temperature and neutralized with 5.5 g of a 20% by weight aqueous calcium hydroxide slurry. The solids content of the resulting aqueous polymer dispersion SDII1 was 54.7% by weight. The dispersed polymer had a glass transition temperature of -1 ° C.

• Inlet I:

  682 g

  n-butyl acrylate

  385 g

  Styrene

  44 g

  a 50 wt .-% aqueous solution of acrylamide

  73.3 g

  a 15 wt .-% aqueous solution of methacrylamide

  16.5 g

  Emulsifier solution 1

  22.6 g

  Emulsifier solution 2 and

  235 g

  Water.

• Inlet II:

  6.4 g

  Sodium peroxydisulfate in

  180 g

  Water.

  SDII2:

  Corresponds to Example 2, DPIIb of EP-A 629650

A mixture of was in a polymerization vessel

500 g

water

2.5 g

Sodium acetate

2.5 g

Butenol and

10 g

an ethoxylated cellulose (Natrosol® 250 GR)

heated to the polymerization temperature of 80 ° C. Then at first 150 g of feed I and then 10 g of feed II were introduced into the polymerization vessel and 20 min. polymerized at 80 ° C. Subsequently, the remaining amount of feed I (within 3 h) and the remaining amount of feed II (within 3.5 h) were metered in continuously while maintaining the 80 ° C. The mixture was then stirred at 80 ° C. for 1 h and finally cooled to room temperature.
The solids content of the resulting aqueous polymer dispersion SDII2 was 50.2% by weight. The dispersed polymer had a glass transition temperature of -2 ° C.

• Inlet I:

  600 g

  Vinyl propionate

  200 g

  tert-butyl acrylate

  200 g

  n-butyl acrylate

  160 g

  a mixture of 150 g of emulsifier solution 1 and 10 g of a block copolymer of ethylene oxide and propylene oxide (molar ratio EO: PO = 0.7 and the relative number average molecular weight = 3200) and

  343 g

  Water;

• Inlet II:

  5 g

  Sodium peroxydisulfate in

  100 g

  Water.

  SDII3:

  Corresponds to Example 3, DPIIc of EP-A 629650

A solution was made in a polymerization vessel

6000 g

water and

17 g

a 45% by weight aqueous solution of the surfactant corresponding to Dowfax® 2A1

heated to the polymerization temperature of 80 ⁰ C. Subsequently, 1087 g of feed I and 108 g of feed II were added in succession to the polymerization vessel and 30 min. polymerized at 80 ° C. Then, while maintaining the polymerization temperature, the remaining amounts of feeds I and II were continuously fed in simultaneously for 3.5 h. The reaction mixture was then left to stand at 80 ° C. for 4 h. Finally, the mixture was cooled to room temperature and neutralized with 420 g of a 25% by weight aqueous sodium hydroxide solution. The solids content of the resulting aqueous polymer dispersion SDII3 was 50.9% by weight. The dispersed polymer had a glass transition temperature of 60 ° C.

• Inlet I:

  12150 g

  Styrene

  2250 g

  Butadiene

  450 g

  a 50% aqueous solution of acrylamide

  375 g

  Acrylic acid

  120 g

  ter-dodecyl mercaptan

  117 g

  a 45% by weight aqueous solution of the surfactant corresponding to Dowfax 2A1

  250 g

  a 15% by weight aqueous solution of the sodium salt of the sulfuric acid half-ester of lauryl alcohol and

  6033 g

  Water.

• Inlet II:

  150 g

  Sodium peroxydisulfate and

  200 g

  Water.

  SDII4:

Like SDII1, but the 385 g styrene was replaced by 385 g methyl methacrylate. After filtration, a dispersion SDII4 with a solids content of 55.6% by weight was obtained. The dispersed polymer had a glass transition temperature of 0 ° C.
d) spray drying the aqueous polymer dispersions from c) and assessing the redispersibility of the resulting powders
First, the respective aqueous polymer dispersion SDII1 to SDII4 was diluted to a solids content of 36.2% by weight. Then, in the aqueous solution of EPI1 from a) or in the aqueous dispersion of VPI from a), so much of the respective polymer dispersion SDII1 to SDII4 diluted to 36.2% by weight was rapidly stirred into the aqueous dispersion of VPI from a) that an aqueous mixture resulted, which had a solids content of 35% by weight (based on the particular dispersed polymer II, 4.5% by weight of EPI1 or VPI were therefore always present).
The spray drying of the aqueous mixtures was carried out in a minor laboratory dryer from GEA Wiegand GmbH (Niro division), DE, with two-component atomization at a tower inlet temperature of 130 ° C and an outlet temperature of 60 ° C (output: approx. 2 kg Spray food / h). As an anti-blocking agent, approx. 2.5% by weight (based on the solid polymer mixture) of a finely divided silica (average grain size diameter: 10 μm) were metered into the drying chamber. Table 1 shows the assessment of the respective spray drying.
The procedure for checking the redispersibility of the polymer powders obtained was as follows:
90 g of water were weighed into a glass bottle and 10 g of polymer powder were added at 25 ° C. The mixture was treated with an Ultra-Turrax 1 from Janke & Kunkel, IKA Labortechnik, Staufen DE, for 1 min. at 9500 rpm. stirred and filled into a measuring cylinder. The measuring cylinder, which was sealed with a plastic drop, was then stored immobile at 25 ° C. for 72 h. The redispersion was then shaken well and filtered through a 72 μm sieve. The sieve containing the filter cake was stored in the drying cabinet at 80 ° C. for 12 hours and then determined by weighing the percentage by weight of the dried coagulum, based on the amount of powder used (10 g). The results are also shown in Table 1. Table 1 Spray dried mixture Wall covering Powder yield Coagulum Dispersion Spraying aids SDII1 EPI1 little 86% 0.5% by weight SDII2 EPI1 little 74% 1.4% by weight SDII3 EPI1 little 63% 2.2% by weight SDII4 EPI1 little 89% 0.7% by weight SDII1 VPI1 strong 30% 7.1% by weight
e) Preparation of aqueous dispersions of polymers II which contain a low molecular weight polymer I according to the invention as the essentially sole dispersant, spray drying of such aqueous polymer dispersions and comparative experiments

• D1:
  200 g of n-butyl acrylate, 200 g of methyl methacrylate and 91.4 g of the 19.7% strength by weight aqueous solution of the polymer EPI1 from a) were emulsified in a feed 1 in 114 g of water. 12 g sodium peroxodisulfate and 159 g water formed feed 2.
  Under an inert gas atmosphere, 200 g of water and 5% by weight of feed 1 were placed in a polymerization vessel. The initial charge was heated to 90 ° C. with stirring and 10% by weight of feed 2 were added. The reaction mixture was then 15 min. kept at 90 ° C. The remaining amount of feed 1 (within 2 hours) and the remaining amount of feed 2 (within 2.5 hours) were then fed continuously to the polymerization vessel. After the feeds had ended, the reaction mixture was stirred for a further 2 hours at 90 ° C. and then cooled to room temperature. The aqueous polymer dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 43.6% by weight, a pH of its aqueous dispersion medium of 1.9 and an LD value of 6% (the LD Value is a measure of the polymer particle size of an aqueous polymer dispersion; it indicates the light transmittance at 25 ° C. in the state diluted to a solids content of 0.01% by weight, relative to pure water and with a layer thickness of 2.5 cm, under the influence of white light). 0.2 g of coagulate remained in the filter. A wet film, coated with a layer thickness of 60 μm, on a glass plate showed essentially no specks (microcoagulate).
• D2:
  Like D1, with the difference that feed 1 consists of an emulsion of 208 g of n-butyl acrylate, 180 g of methyl methacrylate, 8 g of acrylamide, 4 g of acrylic acid and 91.4 g of the 19.7% strength by weight aqueous solution of the polymer EPI1 consisted of a) in 114 g of water. The dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 43.9% by weight, a pH of its aqueous dispersion medium of 4.3 and an LD value of 52%. 0.2 g of coagulate remains in the filter. A wet, at a film thickness of 60 µm on a glass plate showed essentially no specks.
• D3:
  Like D1, with the difference that feed 1 consists of an emulsion of 248 g of n-butyl acrylate, 140 g of styrene, 8 g of acrylamide, 4 g of methacrylamide and 91.4 g of the 19.7% strength by weight aqueous solution of the polymer EPI1 consisted of a) in 114 g of water. The dispersion obtained after filtrating through a sieve with a mesh size of 250 μm had a solids content of 43.3% by weight, a pH of its aqueous dispersion medium of 2.1 and an LD value of 49%. 0.3 g of coagulate remains in the filter. A wet film, coated with a layer thickness of 60 μm, on a glass plate showed essentially no specks.
• D4:
  A feed 1 was formed from a mixture of 100 g of n-butyl acrylate and 100 g of methyl methacrylate. A solution of 1.0 g of hydrogen peroxide and 100 g of water formed an inlet 2. Under an inert gas atmosphere, 247 g of water, 1.3 g of a 15% strength by weight aqueous sodium lauryl sulfate solution, 50.8 g of a 19 g, were placed in a polymerization vessel. 7% by weight aqueous solution of the polymer EPI1 from a), 0.04 g of CuSO ₄ .5H ₂ O and 5% by weight of feed 1. The initial charge was heated to 85 ° C. with stirring and 10% by weight of feed 2 were added. The mixture was then kept under stirring for 15 min at 85 ° C. and then, while maintaining the 85 ° C., the remaining amounts of feed 1 (within 2 h) and feed 2 (within 2.5 h) were simultaneously fed continuously into the polymerization vessel. After the feed had ended, the polymerization mixture was stirred for a further 2 h at 85 ° C. and then cooled to room temperature. The dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 34.2% by weight, a pH of its aqueous dispersion medium of 6.8 and an LD value of 88%. 0.69 g of coagulate remained in the filter. A wet film, coated with a layer thickness of 60 μm, on a glass plate showed essentially no specks.
• D5:
  An emulsion was formed from 155 g of n-butyl acrylate, 87.5 g of styrene, 5 g of acrylamide, 2.5 g of methacrylamide, 190.4 g of the 19.7% by weight solution of the polymer EPI1 from a) and 20 g of water formed as inlet 1. A solution of 7.5 g of sodium peroxodisulfate in 100 g of water formed an inlet 2. Under an inert gas atmosphere, 104 g of water and 5% by weight of inlet 1 were placed in a polymerization vessel. The initial charge was heated to 90 ° C. with stirring and 10% by weight of feed 2 were added. The mixture was then 15 min. kept at 90 ° C with stirring. The remaining amounts of feed 1 (within 2.0 h) and of feed 2 (within 2.5 h) were then fed continuously to the polymerization vessel while maintaining the 90 ° C. The reaction mixture was then stirred at 90 ° C. for a further 2 h and finally cooled to room temperature.
  The dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 43.2% by weight, a pH of its aqueous dispersion medium of 2.7 and an LD value of 68%. 0.3 g of coagulate remained in the filter. A wet film scraped onto a glass plate in a layer thickness of 60 μm showed essentially no specks.
• VD1:
  Like D1, feed 1, however, consisted of an emulsion of 200 g of n-butyl acrylate, 200 g of methyl methacrylate and 90 g of the 20% by weight aqueous dispersion of the polymer VPI from b) in 114 g of water. The dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 43.4% by weight, a pH of its aqueous dispersion medium of 1.7 and an LD value of 30%. 5.8 g of coagulate remained in the filter. A wet film, coated with a layer thickness of 60 µm, on a glass plate showed numerous specks.
• VD2:
  Like D5, but instead of the 190.4 g of the 19.7% strength by weight aqueous solution of the polymer EPI1 from a), 187.5 g of the 20% strength by weight aqueous dispersion of the polymer VPI from b) were used. The dispersion obtained after filtration through a sieve with a mesh size of 250 μm had a solids content of 42.7% by weight, a pH of their aqueous dispersing medium of 2.1 and an LD of 43%. 14 g of coagulum remained in the filter. A wet film, coated with a layer thickness of 60 µm, on a glass plate showed numerous specks.
• VD3:
  Like D4, but the template contained a mixture of 247 g of water, 1.3 g of a 15% by weight aqueous sodium lauryl sulfate solution, 50 g of a 20% by weight aqueous solution of a poly-2 prepared in analogy to a) Acrylamido-2-methylpropanesulfonic acid, the weight-average relative molecular weight of which was 38,000, 0.04 g of CuSO ₄ .5H ₂ O and 5% by weight of feed 1. The reaction mixture already thickened during the monomer feed, so that the reaction batch had to be stopped .
• VD4:
  Like D1, feed 1, however, consisted of 200 g of n-butyl acrylate, 200 g of methyl methacrylate, 90 g of the 20% by weight aqueous poly-2-acrylamido-2-methyl-propanesulfonic acid solution from VD3 and 116 g of water. The batch coagulated after the polymerization.
• VD5:
  Like D1, feed 1, however, consisted of 200 g of n-butyl acrylate, 200 g of methyl methacrylate, 71.2 g of a 25.3% strength by weight aqueous solution of Sokalan® CP9 (maleic acid copolymer), which is used as a dispersant for finely divided organic and inorganic solids is commercially available and 135 g of water. The batch coagulated after the polymerization. This indicates that dispersants for finely divided organic and inorganic solids are not necessarily suitable as protective colloids for carrying out free-radical aqueous emulsion polymerizations.
  The aqueous polymer dispersions D1 to D5 could be dried satisfactorily to redispersible polymer powders by the spray drying process described under d).

f) Preparation of further polymers I (EPI2 to EPI6) to be used according to the invention and aqueous dispersions D6 to D10 of polymers II which are essentially the only ones Dispersant contain a low molecular weight polymer I according to the invention and the spray drying of such aqueous polymer dispersions.
1. Production of EPI2 to EPI6
The polymerizations were carried out under inert gas. 810 g of water were initially placed in a polymerization vessel and heated to 85.degree. While maintaining this temperature, 10% by weight of a solution of Xg sodium peroxodisulfate in Yg water was added and the mixture was stirred for 5 minutes. The remaining amount of sodium peroxodisulfate solution and, spatially separated therefrom, a mixture of 800 g of water, 400 g of 2-acrylamido-2-methylpropanesulfonic acid, 400 g of a 25% by weight aqueous sodium hydroxide solution and 0.04 were then kept at 85 ° C. g of 4-methoxyphenol, with stirring (both feeds starting simultaneously), continuously fed to the polymerization vessel over the course of two hours. The reaction mixture was then stirred for a further hour at 85 ° C. and then cooled. Table 1 below shows the values used for X and Y, the solids contents of the resulting aqueous solutions, the pH values of the associated aqueous dispersing media and the weight-average relative molecular weight M _{w of} the polymers EPI2 to EPI6 in solution. X Y Solids content (% by weight) PH value M _w EPI2 2.4 100 19.3 13.5 12300 EPI3 5 110 19.2 13.4 11400 EPI4 10th 130 19.4 13.4 10,000 EPI5 20th 170 19.5 13.2 9600 EPI6 40 250 19.3 12.9 8500
2. Preparation of aqueous dispersions D6 to D10 of polymers II and their spray drying
208 g of n-butyl acrylate, 180 g of methyl methacrylate, 8 g of acrylamide, 4 g of acrylamide and 18.0 g of one of the polymers EPI2 to EPI6 were emulsified in a feed 1 in 187 g of water and the resulting emulsion was dissolved in a 2N aqueous NH ₃ solution adjusted to pH 8.0. The solution of 12.0 g sodium peroxodisulfate in 159 g water formed feed 2.
200 g of water and 5% by weight of feed 1 were placed in a polymerization vessel under an inert gas atmosphere. The initial charge was heated to 90 ° C. with stirring and 10% by weight of feed 2 were added. The reaction mixture was then kept at 90 ° C. for 15 minutes. The remaining amount of feed 1 (within 2 hours) and the remaining amount of feed 2 (within 2.5 hours) were then fed continuously to the polymerization vessel. After the feeds had ended, the reaction mixture was stirred for a further 2 h at 90 ° C. and then cooled to room temperature. The solids content, the pH of the aqueous dispersion medium and its LD value and the coagulum content in the filter were determined from the aqueous polymer dispersions obtained after filtration through a sieve with a mesh size of 250 μm. In addition, a wet film of 60 μm was knife-coated onto a glass plate from the filtered aqueous polymer dispersions and the proportion of specks thereon was assessed qualitatively (essentially = essentially). The results obtained are shown in Table II. Polymer I Solids content [% by weight] LD [%] Coagulum [g] Quilting pH D6 EPI2 43.6 52 0.2 iw none 4.7 D7 EPI3 43.1 53 0.5 iw none 4.6 D8 EPI4 43.2 42 0.7 iw none 4.5 D9 EPI5 43.8 34 0.6 iw none 4.4 D10 EPI6 43.6 45 0.5 iw none 4.4

The aqueous polymer dispersions D6 to D10 could be dried satisfactorily to redispersible polymer powders by the spray drying process described under d).

Claims (33)

Drying an aqueous dispersion of a polymer II, characterized in that the aqueous dispersion of the polymer II contains at least one polymer I added as drying aid, which is in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and
0 to <20% by weight of at least one radically copolymerizable monomer (monomers b)
is constructed. Drying according to claim 1, characterized in that the polymer I in polymerized form is composed of 90 to 100% by weight of monomers a and 0 to 10% by weight of monomers b. Drying according to claim 1, characterized in that the polymer I in polymerized form is composed solely of monomers a. Drying according to one of claims 1 to 3, characterized in that the polymer I contains 2-acrylamido-2-methylpropanesulfonic acid and / or the salts thereof in copolymerized form. Drying according to claim 3, characterized in that the polymer I in polymerized form is composed solely of 2-acrylamido-2-methylpropanesulfonic acid and / or its salts. Drying according to one of claims 1 to 5, characterized in that the relative weight-average molecular weight of the polymer I is 1000 to 10 ⁶ . Drying according to one of claims 1 to 5, characterized in that the relative weight-average molecular weight of the polymer I is 2000 to 45000. Drying according to one of claims 1 to 7, characterized in that the solubility of the polymer I in 100 g of water at 25 ° C and 1 bar is at least 10 g. Drying according to one of claims 1 to 8, characterized in that the aqueous dispersion of polymer II, based on the mass of polymer II, contains 1 to 40% by weight of polymer I. Drying according to one of claims 1 to 8, characterized in that the aqueous dispersion of polymer II, based on the mass of polymer II, contains 1 to 20% by weight of polymer I. Drying according to one of claims 1 to 8, characterized in that the aqueous dispersion of polymer II, based on the mass of polymer II, contains 1 to 5% by weight of polymer I. Drying according to one of claims 1 to 11, characterized in that the glass transition temperature of the polymer II is ≤ 50 ° C. Drying according to one of claims 1 to 12, characterized in that the polymer II in polymerized form A) 80 to 100% by weight of at least one monomer from the group comprising styrene, α-methylstyrene, vinyltoluenes, esters of 3 to 6 C-atom-containing α, β-monoethylenically unsaturated carboxylic acids and 1 to 12 C-atom alkanols, Butadiene and vinyl and allyl esters of 1 to 12 carbon atoms and carboxylic acids B) 0 to 20% by weight of other monomers having at least one ethylenically unsaturated group is constructed. Drying according to one of claims 1 to 13, characterized in that the drying is carried out by the spray drying method. Drying according to claim 14, characterized in that the inlet temperature of the warm air flow is 100 to 200 ° C and the outlet temperature of the warm air flow is 30 to 90 ° C. Use of polymers I in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and
0 to <20% by weight are composed of at least one free-radically copolymerizable monomer (monomers b), as an aid in the drying of aqueous dispersions of polymers II different from the polymers I. Polymer powder containing at least one polymer I in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and is composed of 0 to <20% by weight of at least one free-radically copolymerizable monomer (monomer b), and at least one polymer II different from polymer I. Polymer powder according to claim 17, which, based on the amount of polymer II contained, contains ≤ 1 wt .-% of emulsifiers. Mineral binder containing at least one polymer powder according to claim 17 or 18. Use of polymer powders according to claim 17 or 18 in preparations for coating or gluing. Synthetic resin plaster dry preparation containing at least one polymer powder according to claim 17 or 18. Aqueous polymer dispersion of a polymer II, the emulsifier content of which is 2 2% by weight and which contains at least one polymer I added as a dispersant, in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and
0 to <20% by weight is composed of at least one free-radically copolymerizable monomer (monomer b) and has a relative weight-average molecular weight of 5,000 to 35,000. An aqueous polymer dispersion according to claim 22, wherein the relative weight average molecular weight of the polymer I is 7500 to 20,000. Aqueous polymer dispersion according to claim 22 or 23, wherein the polymer I is poly-2-acrylamido-2-methylpropanesulfonic acid. An aqueous polymer dispersion according to any one of claims 22 to 24, wherein the polymer I forms the only dispersant contained. Aqueous polymer dispersion according to one of Claims 22 to 25, the weight-average polymer particle diameter of which is ≥ 50 to ≤ 200 nm. Use of an aqueous polymer dispersion according to any one of claims 22 to 26 as a binder or as an additive in mineral binders. Use of an aqueous polymer dispersion according to one of claims 22 to 26 for the preparation of polymer powders. Use of an aqueous dispersion of a polymer II, which contains a polymer I different from this polymer II, added in polymerized form
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and
0 to <20% by weight is composed of at least one free-radically copolymerizable monomer (monomer b),
for the production of polymer powders. Process for the free radical aqueous emulsion polymerization of monomers having at least one ethylenically unsaturated group, characterized in that a polymer I, which is in polymerized form, is added before, during or after the end of the polymerization
> 80 to 100% by weight of at least one monomer of the general formula I and / or salts thereof (monomers a)

With R ¹ , R ² , R ³ : independently of one another H or C ₁ - to C ₃ -alkyl, R ⁴ : C ₁ to C ₅ alkylene and X: O or NH, and
0 to <20% by weight is composed of at least one free-radically copolymerizable monomer (monomer b) and its relative weight-average molecular weight is 5,000 to 35,000. A method according to claim 30, characterized in that the polymer I contains no monomers b polymerized. A method according to claim 30 or 31, characterized in that the polymer I forms the only dispersant added during the free radical aqueous emulsion polymerization. Polymer powder obtainable by drying according to one of claims 1 to 15.